Method for estimating doppler frequency

ABSTRACT

Disclosed is a method for estimating a Doppler frequency with phase information, thereby estimating a maximum Doppler frequency. The method for estimating the Doppler frequency includes the steps of measuring phases of phase samples from a plurality of slots of a received signal, evaluating a phase difference of the measured phase, and estimating a maximum Doppler frequency according to a mean of at least one phase difference.

This application claims the benefit of the Korean Application No.P2002-81721 filed on Dec. 12, 2002, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication technology, andmore particularly, to a method for estimating a Doppler frequency withphase information, thereby estimating a maximum Doppler frequency.

2. Discussion of the Related Art

According as frequency resource becomes important in mobilecommunication technology, adaptive receiver techniques have been paidmuch attention to an efficient usage of the frequency resource and aflexible resource management. There are a lot of factors to optimize aperformance of the adaptive receiver. Above all, to estimate a maximumDoppler frequency is one of the most valuable factors. The maximumDoppler frequency has been estimated according to the variation of themeasured pilot signal strength. However, the method for estimating amaximum Doppler frequency may have errors in case of that the adaptivereceiver has a great Gaussian noise or a very high Doppler frequency.

In a communication system using a Phase Shift Keying (PSK) modulation ofa non-coherent method, a maximum Doppler frequency is also estimatedbased on variations of the received signal strength. Particularly, incase of a communication system using Differential Phase Shift Keying(DPSK) modulation, because a pilot signal is not transmitted to areceiver, the receiver may estimate a maximum Doppler frequency usingvariations of another received signal such as traffic signal.

However, if the aforementioned method for estimating the maximum Dopplerfrequency with variations of a power for the received signal is appliedto CDMA system using a rapid closed loop power control method, it hasproblems decreasing an accuracy in the estimating of a maximum Dopplerfrequency.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forestimating Doppler frequency that substantially obviates one or moreproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide to a method forestimating Doppler frequency for improving accuracy in the estimate ofthe maximum Doppler frequency with phase variations (phase differences)of received signals.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for estimating a Doppler frequency, comprises the steps ofmeasuring phases of phase samples from a plurality of slots of areceived signal, evaluating a phase difference of the measured phase,and estimating a Doppler frequency according to a mean of at least onephase difference.

In another aspect of the present invention, a method for estimating aDoppler frequency, comprises the steps of measuring phases of phasesamples for successive slots of a demodulated pilot signal at eachpredetermined period τ, evaluating a phase difference of the phasesmeasured at the period τ, evaluating a mean of an absolute phasedifference, and estimating a maximum Doppler frequency with the mean ofthe absolute phase differences and the period τ.

In still another aspect of the present invention, a method forestimating a Doppler frequency, comprises the steps of extracting phasesamples for each of successive slots of a phase shift keying (PSK)demodulated signal, compensating the phases of a portion of the phasesamples for each of the successive slots, evaluating a mean phase of thephase samples for each of the successive slots, evaluating respectivedifferences of mean phases for every successive slots, evaluating a meanof absolute values of the differences, and estimating a maximum Dopplerfrequency with the mean of the absolute values and a period τ ofextracting the phase samples.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram illustrating a method for estimating a maximumDoppler frequency according to the first preferred embodiment of thepresent invention;

FIG. 2 is a diagram illustrating a method for estimating a maximumDoppler frequency according to the second preferred embodiment of thepresent invention;

FIG. 3 illustrates standard constellation of a transmitted DPSKmodulated signal; and

FIG. 4 illustrates standard constellations of a received DPSKdemodulated signals for at least two successive slots.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Even though the present invention is illustrated withreference to the preferred embodiments, the present invention is notlimited to the following preferred embodiments. That is, the presentinvention may include variations if they come within the scope of themain technology of the present invention.

In a method for estimating a maximum Doppler frequency according to afirst preferred embodiment of the present invention, a phase differenceof phases measured at each predetermined period τ is calculated, and amean of phase differences calculated from the measured phases iscalculated. And then, a maximum Doppler frequency is estimated from thecalculated mean phase difference.

Especially, the present invention may be adapted to a communicationsystem which does not transmit a pilot signal. That is, in acommunication system transmitting a pilot signal, a maximum Dopplerfrequency is estimated based on phase variations in slots of the pilotsignal. Meanwhile, a communication system, in which a pilot signal isnot transmitted, uses phase differences in slots of a demodulatedtraffic signal to estimate the maximum Doppler frequency.

A method for estimating a maximum Doppler frequency according to a firstpreferred embodiment of the present invention includes following foursteps.

-   -   1. Measure phases ( . . . , φ_(i−1), φ_(i), . . . ) of phase        samples from a plurality of slots in a received signal at each        predetermined period τ. At this time, the received signal may be        a pilot signal demodulated according to a coherent method, and a        PSK demodulated signal (DPSK demodulated signal or BPSK        demodulated signal) according to a non-coherent method.    -   2. Evaluate a phase difference φ_(i−1)−φ_(i) between the phase        samples measured for every at least two successive slots. And        then, an absolute phase difference |φ_(i)−φ_(i−1)| is evaluated.    -   3. Evaluate a mean Z of absolute phase differences as follows.

${\hat{f}}_{D} = \frac{Z}{\sqrt{2}{\pi\tau}}$

-   -   4. Apply the mean Z of the absolute phase differences to the        following equation

$Z =  {\frac{1}{N}\sum\limits_{n = 0}^{N}}\; \middle| {\phi_{n} - \phi_{n - 1}} |$where

$\frac{1}{\sqrt{2}}$is a constant value used for estimating a maximum Doppler frequency inurban environments, and the constant value may vary based on a place ofestimating a Doppler frequency. Therefore, the maximum Doppler frequency(f_(D)) is estimated.

FIG. 1 is a diagram illustrating a method for estimating a maximumDoppler frequency according to the first preferred embodiment of thepresent invention. That is, FIG. 1 illustrates the method for estimatingthe maximum Doppler frequency with a phase variation of a pilot signal.

Referring to FIG. 1, phases ( . . . , φ_(i−1), φ_(i), . . . ) of phasesamples are measured from a demodulated pilot signal at eachpredetermined period τ (S1). Subsequently, a phase difference of the twosuccessive phase samples is evaluated (S2). The phase difference (ζ_(i))of the at least two successive phase samples is expressed as followingEquation 1.ζ_(i)=φ_(i)−φ_(i−1)  [Equation 1]When ζ_(i) is a phase difference φ₂−φ₁ of the respective phasesφ₂=φ(t+τ) and φ₁=(t), ζ satisfying −π<ζ<π, the probability densityfunction P(ζ) of ζ is expressed as following Equation 2. At this time,the following Equation 2 is an example of a probability density functionof ζ in urban environments.

$\begin{matrix}{{P(\zeta)} = {\frac{1 - \lambda^{2}}{2\pi} \cdot \frac{\sqrt{1 - {\lambda^{2}\cos^{2}\zeta}} + {{\lambda cos\zeta cos}^{- 1}( {- {\lambda cos\zeta}} )}}{( {1 - {\lambda^{2}\cos^{2}\zeta}} )^{3/2}}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

In the above Equation 2, λ=J₀(2πf_(Dτ)). At this time, f_(D) is amaximum Doppler frequency.

Next, a mean of absolute phase differences evaluated at eachpredetermined period τ is evaluated (S3). Meanwhile, a mean E(|ζ|) of anabsolute phase difference of ζ denoting a phase difference of the phasesamples can be expressed as following Equation 3.

$\begin{matrix}{ {{E( |\zeta| )}==\int_{0}^{\pi}} \middle| \frac{\xi}{\pi} \middle| {{P(\zeta)}\ {\mathbb{d}\zeta}}  = {\int_{0}^{\pi}{\frac{\zeta}{\pi}{( {1 - \lambda^{2}} ) \cdot \frac{1 - \lambda^{2}}{2\pi} \cdot \frac{\sqrt{1 - {\lambda^{2}\cos^{2}\zeta}} + {{\lambda cos\zeta cos}^{- 1}( {- {\lambda cos\zeta}} )}}{( {1 - {\lambda^{2}\cos^{2}\zeta}} )^{3/2}}}\ {\mathbb{d}\zeta}}}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$In Equation 3, the mean E(|ζ|) of the absolute phase differences of ζdenoting the phase difference of the phase samples is directly relatedto a maximum Doppler frequency f_(D).

A mean of absolute phase differences evaluated from ‘N’ phase samples isevaluated as following Equation 4.

$\begin{matrix}{Z =  {\frac{1}{N}\sum\limits_{n = 0}^{N}}\; \middle| {\phi_{n} - \phi_{n - 1}} \middle| {{E( |\zeta| )} \approx Z_{Narrow\infty}} } & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$In the above Equation 4, as ‘N’ is larger, ‘Z’ converges to E(|ζ|). Thatis, ‘Z’ is the approximation of E(|ζ|) evaluated at each predeterminedperiod τ.

According to Equation 3 and 4, a maximum Doppler frequency f_(D) isrelated with a mean of an absolute phase difference ‘Z’ as shownEquation 5.

$\begin{matrix}{{\hat{f}}_{D} = {K\frac{Z}{\pi\tau}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

In Equation 5, the maximum Doppler frequency is estimated (S4). Also, aconstant value K varies based on a radio environment condition. Forexample, K is

$\frac{1}{\sqrt{2}}$in the urban environments. At this time, a period τ satisfyingf_(Dτ)<0.4 (where)

$K = \frac{1}{\sqrt{2}}$may be marginally set to estimate a maximum Doppler frequency in a highDoppler frequency region. In this state, ‘Z’ obtains an accuracy of theapproximation when satisfying f_(Dτ)<0.4.

The first preferred embodiment of the present invention using a phasedifference of a demodulated pilot signal does not have any performancedegradation in a communication system using the closed loop powercontrol like CDMA system. Accordingly, if the first preferred embodimentof the present invention is applied to the CDMA system, an accuracy inestimating of a maximum Doppler frequency is improved.

However, in a communication system using a PSK modulation/demodulationof the non-coherent method, a pilot signal is not transmitted. A methodfor estimating a maximum Doppler frequency in the communication systemthat does not transmit the pilot signal will be described as follows.

FIG. 2 is a diagram illustrating a method for estimating a maximumDoppler frequency according to the second preferred embodiment of thepresent invention. FIG. 2 illustrates a case applied to a communicationsystem using a PSK modulation/demodulation of the non-coherent method,especially in the communication system using a DPSKmodulation/demodulation. Thus, a maximum Doppler frequency is estimatedwith a mean of phase differences of a PSK demodulated signal. Also, amethod for estimating a maximum Doppler frequency according to thesecond preferred embodiment of the present invention may be applied to acommunication system using a BPSK modulation/demodulation.

An estimating procedure of FIG. 2 will be explained with reference toFIG. 3 and FIG. 4. FIG. 3 illustrates a standard constellation of atransmitted DPSK modulated signal, and FIG. 4 illustrates a standardconstellation of a received DPSK demodulated signal for at least twosuccessive slots.

When a DPSK modulated signal is “0”, a binary signal value, the DPSKmodulated signal is transmitted without a phase shifting. Meanwhile,when a DPSK modulated signal is “1”, the DPSK modulated signal may havea phase shifting of 180 degrees, and then transmitted.

A constellation of a received DPSK demodulated signal is shown in FIG.3, and a constellation of the received DPSK demodulated signal for atleast two successive slots are shown in FIG. 4. In FIG. 4, therespective constellations means samples of a received signal.

A method for estimating a maximum Doppler frequency according to thesecond preferred embodiment of the present invention will be describedwith reference to FIG. 2.

First, a phase difference is evaluated for being applied to theaforementioned Equations 4 and 5. In fact, it is impossible to evaluatean absolute phase difference |φ_(n)−φ_(n−1)| applied to Equation 4 in acommunication system using a DPSK modulation/demodulation of thenon-coherent method. Thus, the absolute phase difference |φ_(n)−φ_(n−1)|applied to Equation 4 is evaluated through the following first to fifthsteps, and a maximum Doppler frequency is estimated in the sixth step atthe same way as the first embodiment of the present invention.

STEP 1: In FIG. 4 illustrating a constellation of the phase samplesextracted for the ‘i’th slot, most of the phase samples are distributedin two quadrants. That is, the phase samples distributed in one quadrantare transmitted without the phase shifting, and the phase samplesdistributed in the other quadrant are shifted at 180 degrees, and thentransmitted. Thus, in a method for estimating a maximum Dopplerfrequency according to second preferred embodiment of the presentinvention, a dominant quadrant having many phase samples is firstlychecked. At this time, the dominant quadrant may be a quadrant havingthe phase samples transmitted without the phase shifting, or not.

STEP 2: The phase samples are compensated for phases with a phase offsetof 180 degrees so that all of phase samples may be located in thedominant quadrant of FIG. 4. Preferably, in the present invention, thephase samples transmitted from a transmitter without the phase shiftingare distributed in the dominant quadrant, and the phase samplesdistributed in the other quadrant and transmitted from the transmitterwith a phase shifting are compensated with a phase offset of 180 degrees(for compensating the phase of the DPSK modulated signal).

STEP 3: After compensating the phases samples with the phase offset of180 degrees, a mean phase of the phase samples extracted for the ‘i’thslot is evaluated. That is, a mean phase {circumflex over (θ)}_(i) ofthe phase samples for the ‘i’th slot is evaluated.

STEP 4: For the next slot, (i+1)th slot, aforementioned first to thirdsteps are performed to evaluate a mean phase {circumflex over (θ)}_(i+1)of phase samples extracted for the ‘i+1’th slot.

STEP 5: A phase difference Δ{circumflex over (θ)}_(i) is evaluatedbetween the mean phase {circumflex over (θ)}_(i) for the ‘i’th slot andthe mean phase {circumflex over (θ)}_(i+1) for the ‘i+1’th slotaccording to following Equations 6 and 7.

$\begin{matrix}{{\Delta{\hat{\theta}}_{i}} = \begin{bmatrix}{{k_{i} \cdot ( {{\hat{\theta}}_{i + 1} - {\hat{\theta}}_{i}} )},\mspace{11mu}  \text{for}\;||{{\hat{\theta}}_{i + 1} - {\hat{\theta}}_{i}}  \middle| {< |  {{\hat{\theta}}_{i + 1} - {( {{\hat{\theta}}_{i} + \pi} )\text{mod}( {2\pi} )}} || } } \\{{{k_{i} \cdot {\hat{\theta}}_{i + 1}} - {( {{\hat{\theta}}_{i} + \pi} )\text{mod}( {2\pi} )}},\mspace{11mu}  \text{for}\;||{{\hat{\theta}}_{i + 1} - {\hat{\theta}}_{i}}  \middle| {> |  {{\hat{\theta}}_{i + 1} - {( {{\hat{\theta}}_{i} - \pi} )\text{mod}( {2\pi} )}} || } }\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 6} \rbrack \\{k_{i} = \begin{matrix}{1,\;{{\text{if}\mspace{11mu}\alpha_{i}} > \alpha_{thresh}}} \\{0,\;{{\text{if}\mspace{11mu}\alpha_{i}} < \alpha_{thresh}}}\end{matrix}} & \lbrack {{Equation}\mspace{14mu} 7} \rbrack\end{matrix}$

In Equations 6 and 7, K_(i) is a reliability factor, and α_(i) is a meanpower the phase samples extracted for the ‘i’th slot. In Equation 7, areceived signal having a power more than a predetermined threshold value(α_(thresh)) is used for estimating a maximum Doppler frequency.

In equation 6 of the present invention, a modular calculation is usedwith regard to selecting a dominant quadrant in which phase sampleshaving shifted phases are distributed. That is, equation 6 takes intoaccount of compensating for the phase samples with a phase offset of 180degrees, wherein the phase samples are transmitted from a transmitterwithout a phase shifting.

In the second preferred embodiment of the present invention, the abovefirst to fifth steps are repeated ‘N’ times at each predetermined periodτ.

STEP 6: The phase differences calculated ‘N’ times are applied toEquation 4 to evaluate a mean of absolute phase differences calculated‘N’ times. Thus, the evaluated approximation Z is applied to Equation 5,whereby a maximum Doppler frequency is estimated.

In the second preferred embodiment, a phase difference |{circumflex over(θ)}_(i+1)−{circumflex over (θ)}_(i)| of at least two successive slotsis calculated from the respective mean phases {circumflex over (θ)}_(i)and {circumflex over (θ)}_(i+1) of the phase samples evaluated accordingto the third to fourth steps. Next, the phase difference is applied toEquation 4 to evaluate a mean of absolute phase differences, and theevaluated mean of the absolute phase differences is applied to Equation5 to estimate a maximum Doppler frequency.

However, in the present invention, the calculated phase difference isdecreased by the reliability factor k_(i). This reason is that a phasedifference evaluated from a received signal of a low power may generateerrors in estimating a maximum Doppler frequency.

In the second preferred embodiment of the present invention, it ispossible to extract phase information of a radio channel from a DPSKdemodulated signal of the non-coherent method. Also, a maximum Dopplerfrequency is estimated by the extracted phase information.

As mentioned above, a method for estimating a maximum Doppler frequencyaccording to preferred embodiments of the present invention has thefollowing advantages.

In a communication system having a pilot signal, it is possible toimprove accuracy in estimating a maximum Doppler frequency with phasevariations for a plurality of slots of the pilot signal. In case of acommunication system in which a pilot signal is not transmitted(especially, the system using a phase modulation/demodulation of thenon-coherent method), a maximum Doppler frequency is estimated with aphase difference for at least two successive slots of a demodulatedtraffic signal with accuracy.

Especially, even if the method estimating a maximum Doppler frequencywith the statistics of phase differences is applied to a CDMA systemusing a rapidly closed loop power control, accuracy is not impaired inestimating a maximum Doppler frequency because the phase information ofthe received signals is not influenced by the closed loop power control.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for estimating a Doppler frequency, comprising: (a)measuring phases of phase samples from a plurality of slots of areceived signal, the phases measured for the slots at each of aplurality of predetermined periods; (b) evaluating a phase difference ofthe measured phases in at least two slots for each of the periods, toderive a plurality of phase differences; (c) computing a mean of thephase differences; and (d) estimating a Doppler frequency based on themean computed in (c) and a value indicative of a radio environmentcondition.
 2. The method of claim 1, wherein the received signal is apilot signal in the (a) step, thereby measuring the phases of the phasesamples for successive slots of the pilot signal at each predeterminedperiod.
 3. The method of claim 1, wherein the received signal is a phaseshift keying (PSK) modulated signal according to a non-coherent methodin the (a) step, thereby measuring the phases of the phase samples forsuccessive slots of the PSK modulated signal at each predeterminedperiod.
 4. The method of claim 1, wherein (b) includes: evaluating anabsolute phase difference of the measured phases in the at least twoslots for each of the periods.
 5. The method of claim 1, wherein (c)includes computing a mean of absolute values of the phase differencescalculated at each of the predetermined periods; and wherein (d)includes estimating a maximum Doppler frequency based on the evaluatedmean of the absolute phase differences, and the period (τ), and saidvalue indicative of a radio environment condition.
 6. A method forestimating a Doppler frequency, comprising: (a) measuring phases ofphase samples for successive slots of a demodulated pilot signal at eachof a plurality of predetermined periods τ; (b) evaluating a phasedifference of the phases measured at each of the periods τ, to derive aplurality of phase differences; (c) evaluating a mean of absolute valuesof the phase differences; and (d) estimating a maximum Doppler frequencybased on the mean of the absolute values of the phase differences, theperiod τ, and a value indicative of a radio environment condition. 7.The method of claim 6, wherein a mean of absolute phase differences for‘N’ phase samples is evaluated in an approximation as follows in the (c)step:$Z = {\frac{1}{N}{\sum\limits_{n = 0}^{N}\;{{{\phi_{n} - \phi_{n - 1}}}.}}}$8. A method for estimating a Doppler frequency, comprising: (a)measuring phases of phase samples for successive slots of a demodulatedpilot signal at each of a plurality of predetermined periods τ; (b)evaluating a phase difference of the phases measured at each of theperiods τ, to derive a plurality of phase differences; (c) evaluating amean of absolute values of the phase differences; and (d) estimating amaximum Doppler frequency based on the mean of the absolute values ofthe phase differences, and the period τ wherein, in (d), the mean Z ofthe absolute values of the phase differences for ‘N’ phase samples isevaluated according to following equation,$Z = {\frac{1}{N}{\sum\limits_{n = 0}^{N}\;{{{\phi_{n} - \phi_{n - 1}}}.}}}$and wherein the maximum Doppler frequency ({circumflex over (f)}_(D)) isestimated by $\hat{f_{D}} = {K\frac{Z}{\pi\;\tau}}$ where K is aconstant value according to a radio environment condition.
 9. A methodfor estimating a Doppler frequency, comprising: (a) extracting phasesamples for each of successive slots of a phase shift keying (PSK)demodulated signal; (b) compensating the phases of a portion of thephase samples for each of the successive slots; (c) evaluating a meanphase of the phase samples for each of the successive slots; (d)evaluating respective differences of mean phases for every successiveslots; (e) evaluating a mean of absolute values of the differences; and(f) estimating a maximum Doppler frequency with the mean of the absolutevalues and a period τ of extracting the phase samples.
 10. The method ofclaim 9, wherein the PSK demodulated signal is modulated by one of DPSKand BPSK modulation methods.
 11. The method of claim 9, wherein the (b)step comprising: (g) defining one quadrant as a dominant quadrant, thedominant quadrant in which lots of phase samples are distributed; and(h) compensating phases of phase samples which are not distributed inthe main quadrant so that all of phase samples may be distributed in themain quadrant.
 12. The method of claim 11, wherein, if the PSKdemodulated signal is a DPSK demodulated signal in the step (h), phasesof the phase samples which are not distributed in the main quadrant arecompensated at 180 degrees.
 13. The method of claim 9, wherein adifference of the mean phases is evaluated for every successive slots ofthe PSK demodulated signal having a power more than a predeterminedthreshold value (α_(thresh)) in the (d) step.
 14. The method of claim 9,wherein, in the (f) step, a mean of the absolute phase differences for‘N’ phase samples is evaluated according to following equation,$Z = {\frac{1}{N}{\sum\limits_{n = 0}^{N}\;{{{\phi_{n} - \phi_{n - 1}}}.}}}$whereby the maximum Doppler frequency ({circumflex over (f)}_(D)) isestimated by $\hat{f_{D}} = {K\frac{Z}{\pi\;\tau}}$ where K is aconstant value varying according to a radio environment condition. 15.The method of claim 1, wherein said value is a constant value indicativeof the radio environment condition.
 16. The method of claim 1, whereinsaid value is a value indicative of the radio environment condition at apredetermined location.
 17. The method of claim 1, wherein the Dopplerfrequency is further estimated based on a probability density functioncorresponding to a radio environment condition, wherein the radioenvironment condition of the probability density function matches theradio environment condition of said value.
 18. The method of claim 1,wherein the Doppler frequency is a maximum Doppler frequency.
 19. Themethod of claim 1, wherein the Doppler frequency is measured for thereceived signal in a communications receiver operating based on a closedloop power control method.
 20. The method of claim 1, wherein thereceived signal is a pilot signal.
 21. The method of claim 1, whereinthe received signal is a traffic signal.
 22. The method of claim 1,wherein the received signal is a PSK signal.